The invention generally relates to rotary piston machines.
Specifically, the invention relates to rotary piston machines of the type comprising a housing in which at least two pistons are arranged, which are able to revolve together in the housing about an axis of rotation which is fixed with respect to the housing. The pistons are mounted slidingly in a piston cage which is mounted in the housing and revolves together with the pistons about the axis of rotation, wherein the two pistons execute mutually opposing reciprocating motions while revolving about the axis of rotation in order to alternately increase and decrease the volume of a working chamber defined by end faces of the two pistons which are oriented towards one another, and by the piston cage. The axis of rotation runs through the working chamber. The piston cage has a gas exchange opening for the admission and discharge of gas to and from the working chamber.
A rotary piston machine according to the present invention can be used as an internal combustion engine (combustion engine), a pump or a compressor.
In the case when such a rotary piston machine is used as an internal combustion engine, the individual working cycles of induction, compression and ignition of the combustible mixture, and expansion and exhaust of the burnt combustible mixture, are effected by reciprocating motions of at least two pistons between two end positions, the motions of the pistons being derived from their rotary motion about the axis of rotation.
In the case when such a rotary piston machine is used as a compressor the operation is similar, although no combustion process, and accordingly no ignition of a combustible mixture, takes place in the rotary piston machine, and a gas, in particular air, is merely highly compressed.
A rotary piston machine known from WO 2006/089576 A1 has in the housing four pistons which, together with the piston cage, define two working chambers which are arranged opposite one another along the axis of rotation and are oriented towards the end faces of the housing. The cycles of induction, compression, expansion and exhaust take place in each of the two working chambers. In the case when this known rotary piston machine is used as an internal combustion engine, the two working chambers are increased and decreased in the same sense, the cycle sequence of induction, compression, expansion and exhaust being phase-shifted by two cycles from the one working chamber to the other working chamber. In the case when this known rotary piston machine is used as a compressor, the two working chambers are increased and decreased in opposite directions, that is, while the one working chamber is being decreased in volume the other working chamber is increasing in volume.
In both cases the axis of rotation about which the pistons revolve and which, within the meaning of the present description, is to be understood as a geometric axis, runs through both working chambers.
Associated with each of the two working chambers of the known rotary piston machine is a respective gas inlet opening and a respective gas outlet opening in the housing. In the piston cage a respective gas exchange opening is present for each working chamber; each gas exchange opening opens into the respective working chamber and, with each revolution of the piston cage about the axis of rotation, communicates temporarily with the respective gas inlet opening or gas outlet opening, so that a gas exchange can take place into or out of the respective working chamber when the gas exchange opening in the piston cage overlaps with the gas inlet opening or the gas outlet opening in the housing. Over the remaining angular range of rotation of the piston cage about the axis of rotation, the piston cage closes the gas inlet openings and the gas outlet openings in the housing in a gas-tight manner, so that the gas admitted to the particular working chamber—a fuel-air mixture in the case of an internal combustion engine—can be compressed and ignited and can work.
Within the meaning of the present invention the term “gas” should be understood in a general sense and includes, for example, air, a fuel-air mixture, burnt fuel-air mixture or any other fluid.
In the known rotary piston machine the gas exchange opening is arranged in the piston cage laterally or radially at a distance from the axis of rotation.
The advantage of the known rotary piston machine is that no valves are required for the gas exchange between the working chamber or chambers, because the opening and closing of the gas exchange opening is effected solely by the rotation of the piston cage in the housing.
By contrast, in the field of linearly-reciprocating piston engines there is very good experience in controlling the gas exchange into and out of the working chambers of the cylinders by means of valves, in particular so-called tulip valves.
However, rotary disc valve systems for controlling the gas exchange, which present themselves as technically very simple solutions for rotary position machines, in particular for spherical engines such as the known rotary piston machine, are regarded with misgivings in technical circles because relevant experience with such gas exchange control systems over many years is lacking.